Liquid crystal display and method for manufacturing the same

ABSTRACT

A liquid crystal display is provided that includes first and second panels facing each other, an alignment layer disposed on at least one of the first and second panels, a fixing member disposed on the surface of the alignment layer to fix the alignment structure of the alignment layer, and liquid crystal materials disposed between the first and second panels. The liquid crystal materials include liquid crystal molecules that have a pre-tilt angle and are disposed on the alignment layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/019,315, filed on Jan. 24, 2008, and claims priority from and thebenefit of Korean Patent Application No. 10-2007-0043102, filed May 3,2007, which are both hereby incorporated by reference for all purpose asif fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display and a methodfor manufacturing the same.

2. Discussion of the Background

A liquid crystal display (LCD) is one of the most widely used flat paneldisplays. An LCD includes two panels provided with field-generatingelectrodes, such as pixel electrodes and a common electrode, and aliquid crystal (LC) layer interposed therebetween. The LCD displaysimages by applying voltages to the field-generating electrodes togenerate an electric field in the LC layer that determines theorientations of LC molecules in the LC layer to adjust the polarizationof incident light.

The LC molecules of LCDs may be initially aligned in a predetermineddirection through a rubbing process. Also, the liquid crystal moleculesof LCDs may be initially aligned at a pre-tilt angle by rubbing the LCmolecules in a vertical alignment (VA) mode so that the direction inwhich the LC molecules will rotate when an electric voltage is appliedcan be controlled.

The pre-tilt angle may be realized through a contact rubbing method anda light alignment method. The alignment layer may be rubbed by using aroller to which physical pressure is applied in the contact rubbingmethod and the alignment layer may be irradiated by ultraviolet rays inthe light alignment method to form the pre-tilt angle.

However, the alignment force acting on the liquid crystal moleculesdecreases over time in the light alignment method, as compared to thecontact rubbing method, so the initial alignment of the LC molecules maybecome scattered.

SUMMARY OF THE INVENTION

The present invention provides an LCD that may uniformly maintain theinitial alignment of the LC molecules over time.

The present invention also provides a method of manufacturing an LCDthat may uniformly maintain the initial alignment of the LC moleculesover time.

Additional features of the present invention will be set forth in thedescription which follows, and in part will be apparent form thedescription, or may be learned by practice of the invention.

The present invention discloses a liquid crystal display including firstand second panels facing each other, an alignment layer disposed on atleast one of the first and second panels, a fixing member disposed onthe alignment layer, and liquid crystal materials disposed between thefirst and second panels. The fixing member fixes the alignment structureof the surface of the alignment layer, and the liquid crystal materialsinclude liquid crystal molecules having a predetermined pre-tilt angledisposed on the alignment layer.

The present invention also discloses a method for manufacturing a liquidcrystal display including providing a first panel having a firstalignment layer, providing a second panel having a second alignmentlayer, forming an alignment structure in the first and second alignmentlayers by irradiating the alignment layers with linearly polarizedultraviolet rays, and providing a liquid crystal assembly. The liquidcrystal assembly includes the first panel, the second panel, and aliquid crystal layer including a liquid crystal material, a monomer, anda photo initiator disposed between the first and second panels. Themonomers are polymerized by irradiating the liquid crystal layer to forma fixing member on the first alignment layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is an equivalent circuit diagram of a pixel of an LC panelassembly according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic sectional view of the LCD according to theexemplary embodiment of the present invention.

FIG. 3 is a view showing the alignment direction of the LC moleculesaccording to the exemplary embodiment of the present invention.

FIG. 4 is a flow chart showing the sequential steps of a manufacturingprocess of the LC cell for the LCD according to the exemplary embodimentof the present invention.

FIG. 5 is a view showing a light alignment of the LCD according to theexemplary embodiment of the present invention.

FIG. 6 is a view showing the motion of the LC molecules corresponding tothe light alignment of FIG. 5.

FIG. 7 is a schematic sectional view of the LCD according to anotherexemplary embodiment of the present invention.

FIG. 8 is a view showing a light alignment of the LC molecules of theLCD of FIG. 7.

FIG. 9 is a view showing the alignment direction of the LC moleculescorresponding to the light alignment of FIG. 8.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosureis thorough, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the sizes of layers and regions maybe exaggerated for clarity. Like reference numerals in the drawingsdenote like elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent.

Now, an LCD according to an exemplary embodiment of the presentinvention will be described with reference to FIG. 1, FIG. 2, FIG. 3,FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9.

Embodiment 1

FIG. 1 is an equivalent circuit diagram of a pixel of an LC panelassembly according to an exemplary embodiment of the present invention,FIG. 2 is a schematic sectional view of the LCD according to theexemplary embodiment of the present invention, and FIG. 3 is a viewshowing the alignment direction of the LC molecules according to theexemplary embodiment of the present invention.

Referring to FIG. 1 and FIG. 2, an LCD according to the exemplaryembodiment of the present invention includes a lower panel 100, an upperpanel 200 facing the lower panel 100, and an LC layer 3 interposedbetween the panels 100 and 200.

The lower panel 100 includes a plurality of gate lines GL, a pluralityof data lines DL, and a plurality of storage lines SL.

A plurality of switching elements Q are connected to the gate lines GLand the data lines DL, a plurality of LC capacitors Clc are connected tothe switching elements Q, and a plurality of storage capacitors Cst areconnected to the storage lines SL. A single pixel is described in detailbelow.

The switching element Q may be disposed on the lower panel 100 and mayhave three terminals, including a control terminal connected to the gateline GL, an input terminal connected to the data line DL, and an outputterminal connected to the LC capacitor Clc and the storage capacitorCst.

The LC capacitor Clc may have two terminals, including a pixel electrode191 disposed on the lower panel 100 and a common electrode 270 disposedon the upper panel 200. The LC layer 3 disposed between the twoelectrodes 191 and 270 may function as a dielectric of the LC capacitorClc. The pixel electrode 191 may be connected to the switching elementQ, and the common electrode 270 may be supplied with a common voltageVcom and may cover an entire surface of the upper panel 200. Unlike FIG.1 and FIG. 2, the common electrode 270 may be provided on the lowerpanel 100 and at least one of the electrodes 191 and 270 may have a baror stripe shape.

The storage capacitor Cst may be an auxiliary capacitor for the LCcapacitor Clc. The storage capacitor Cst may include the pixel electrode191 and the storage line SL, which may be provided on the lower panel100, may overlap the pixel electrode 191 via an insulator, and may besupplied with a predetermined voltage such as the common voltage Vcom.Alternatively, the storage capacitor Cst may include the pixel electrode191 and an adjacent gate line, i.e., the previous gate line, whichoverlaps the pixel electrode 191 via an insulator.

For a color display, each pixel may uniquely represent one primary color(i.e., spatial division) or each pixel may sequentially represent theprimary colors in turn (i.e., temporal division) such that the spatialor temporal sum of the primary colors may be recognized as a desiredcolor. An example of a set of primary colors is red, green, and blue.FIG. 1 shows an example of spatial division where each pixel includes acolor filter 230 representing one of the primary colors in an area ofthe upper panel 200 facing the pixel electrode 191. Alternatively, thecolor filter 230 may be provided on or under the pixel electrode 191 onthe lower panel 100.

The common electrode 270 may be disposed on the color filters 230, andan overcoat 250 (referring to FIG. 2) to provide a flat surface may beformed between the common electrode 270 and the color filters 230.

The LC layer 3 may be a nematic LC material having negative dielectricanisotropy, and the LC molecules 310 of the LC layer 3 may be aligned ata pre-tilt angle θ of about 88-89 degrees with the surface of thesubstrates 110 and 210 when an electric field is not applied.

Referring to FIG. 3, the initial alignment directions of the LCmolecules 310 may be classified into four directions. One pixel mayinclude four domains having different initial alignment directions ofthe LC molecules 310. The initial alignment directions of the LCmolecules 310 may vary and there may alternatively be three or less orfive or more alignment directions if so needed.

Again referring to FIG. 2, alignment layers 11 and 21 may be coated oninner surfaces of the panels 100 and 200, respectively.

A plurality of fixing members 33 may be respectively formed on thealignment layers 11 and 21. The fixing members 33 may fix the alignmentstate of the alignment layers 11 and 21 to prevent the alignment forceof the alignment layers 11 and 21 from decreasing over time.

Polarizers 12 and 22 may be provided on outer surfaces of the panels 100and 200, respectively, and their polarization axes may be perpendicularto each other.

The LCD may include a plurality of retardation films (not shown) and abacklight unit (not shown) to supply light to the polarizers 12 and 22,the panels 100 and 200, and the LC layer 3.

Now, a method of manufacturing the LCD according to exemplaryembodiments of the present invention will be described with reference toFIG. 4, FIG. 5, and FIG. 6.

FIG. 4 is a flow chart showing the sequential steps of a manufacturingprocess of the LC cell for the LCD according to the exemplary embodimentof the present invention, FIG. 5 is a view showing a light alignment ofthe LCD according to the exemplary embodiment of the present invention,and FIG. 6 is a view showing the motion of the LC moleculescorresponding to the light alignment of FIG. 5.

As shown in FIG. 4, lower and upper mother glasses may be completedthrough processes S100 and S102 and then a plurality of spacers may beformed on one of the upper and lower mother glasses to maintain theuniform interval between the upper and lower mother glasses S104. Thespacers may be bead spacers dispersed with a spherical shape or columnspacers formed by a photolithography process.

Next, a light alignment process may be executed by irradiating thealignment layers formed on the upper and lower mother glasses withlinearly polarized ultraviolet (LPUV) rays (S106).

Here, the irradiation with LPUV rays may be performed using a mask suchthat only portions of the alignment layers are irradiated by the LPUVrays. Also, the LPUV rays may be directed at the alignment layers at atilted angle with respect to the surface of the alignment layers so thatthe alignment layers may be rubbed in a predetermined direction. Toirradiate with the LPUV rays at the tilted angle, the upper and lowermother glasses may be tilted or the device for irradiating with the LPUVrays may be tilted.

Because the alignment direction of the alignment layer may be changedaccording to the direction of the irradiating LPUV rays, one pixel maybe divided into a plurality of sub regions that are irradiated by LPUVrays at different directions. For example, one pixel may include aplurality of domains having LC molecules with different pre-tiltdirections.

To align the LC molecules 310 with four initial alignment directions asshown in FIG. 3, referring to FIG. 5, the upper half of the pixel regionin the lower panel may be irradiated by the LPUV rays from right to leftto form a pre-tilt angle, and the lower half of the pixel region in thelower panel may be irradiated by the LPUV rays from left to right toform a pre-tilt angle. Also, in the upper panel, the left half of thepixel region may be irradiated by the LPUV rays from top to bottom toform a pre-tilt angle, and the right half of the pixel region may beirradiated by the LPUV rays from bottom to top to form a pre-tilt angle.

When executing the light alignment by this method, as shown in FIG. 6,the alignment directions of the LC molecules (represented with solidlines and dotted lines) may be changed as represented by the thick arrowlines extending from the lower panel to the upper panel. Also, fourdomains having different initial alignment directions of the LCmolecules are formed in one pixel.

The pre-tilt angle of the LC molecules may be changed according to theenergy level of the LPUV rays, and the pre-tilt angle of the LCmolecules may be decreased when the energy level of the LPUV rays isincreased. Accordingly, the pre-tilt angle of the LC molecules may becontrolled by controlling the energy level of the LPUV rays. Thepre-tilt angle of the LC molecules may be in the range of 88-89 degreesin the exemplary embodiment according to the present invention.

Next, a sealing member to define the portion where the LC layer isformed and to prevent leakage of the LC layer may be formed on one ofthe two panels (S108). The sealing member may include a material thatcan be hardened by ultraviolet rays to combine the two panels.

Next, mixtures including LC molecules, a photo initiator, and monomersthat may be polymerized by light may be drip formed on one of the twopanels (S110).

The monomers may be injected in an amount such that the monomersinterfere with the movement of the LC molecules after forming the fixingmember. The monomers may include an acrylate based compound, and thecontent of the monomers may be in the range of 0.01-10 wt % with respectto the content of the LC molecules. Also, the content of the photoinitiator may be in the range of 0.01-0.05 wt % with respect to thecontent of the LC molecules. Such an amount of photo initiator may causethe polymerization reaction of the monomer and the photo initiator mayinclude 2,2-dimethoxy-1,2-diphenyl ethanone.

Next, the sealing member may be irradiated to harden the sealing memberdisposed between the two mother glasses after combining the two motherglasses (S200) to complete an LC assembly.

Here, a mask may be used to selectively irradiate the sealing member.

Next, the LC assembly may be divided into a plurality of LC cells byscribing the LC assembly according to a cutting line (S202).

Next, ultraviolet rays may vertically irradiate the LC cell to form aplurality of fixing members (S204). The ultraviolet rays may be LPUVrays. The LPUV rays may irradiate the front side or the rear side of theLC cell or the front side and the rear side may be irradiatedsimultaneously. The intensity of the LPUV rays may be in the range of2-20 J/cm².

Here, the monomers may be polymerized by the photo initiator and thepolymerized polymer may be adhered to the surface on the alignmentlayers to form the fixing member.

On the other hand, a voltage of 2-20 V may be applied to the two panelswhen irradiating light. The voltage may be applied using visual pads orother pads, and an alternating current or a direct current may be used.The applied voltage may increase the control force so that the monomersin the LC layer may be easily moved and then the polymerization reactionmay be improved.

In an alternative LC injection method for injecting the LC materialbetween the two panels, the plurality of LC cells may be divided andthen the LC material may be injected between the two panels. Then the LCcells may be irradiated.

Embodiment 2

FIG. 7 is a schematic sectional view of the LCD according to anotherexemplary embodiment of the present invention, FIG. 8 is a view showingthe light alignment of the LC molecules of the LCD of FIG. 7, and FIG. 9is a view showing the alignment direction of the LC moleculescorresponding to the light alignment of FIG. 8.

Because the structure of the LC display shown in FIG. 7 is the same asthat shown in FIG. 2, a description of elements that are the same isomitted.

The LC display shown in FIG. 7 includes four domains having different LCmolecule 31 directions in each pixel, like FIG. 2. However, thealignment directions of the LC molecules 31 are different than that ofFIG. 2, as is the method for aligning the different directions of the LCmolecules 31.

In this exemplary embodiment, as shown in FIG. 8, the direction of thelight alignment of an upper panel may be the same as the direction ofthe light alignment of a lower panel. That is to say, the lightalignment may be executed to form a pre-tilt angle with an obliquedirection from the four corners of each pixel electrode 191 to thecenter of each pixel electrode 191.

Therefore, as shown in FIG. 9, the LC molecules 31 may be aligned on aslope from the four corners of each pixel electrode 191 to the center ofeach pixel electrode 191 such that four domains having different initialalignment directions of the LC molecules 31 are formed.

As above described, the light alignment may be used to align the LCmolecules with various directions without the need for patterning of thepixel electrodes. As such, a wide viewing angle may be obtained.

Furthermore, because the pixel electrodes and the common electrode donot need to be patterned, the electric charges may be amassed inarbitrary positions. Accordingly, damage to the polarizers due toelectric charges may be prevented and a process for removing theelectrostatic charges to prevent damage of the polarizers may beomitted.

Furthermore, fixing members may be formed on the surface of thealignment layers so that the initial light alignment of the alignmentlayers is scattered. Accordingly, the quality of the LC display may beimproved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display panel, comprising: a first panel and asecond panel facing each other; a first alignment layer disposed on thefirst panel; a second alignment layer disposed on the second panel; andliquid crystal materials disposed between the first panel and the secondpanel, wherein the liquid crystal materials comprise liquid crystalmolecules having a pre-tilt angle in a range of 88-89 degrees and aredisposed on the first and the second alignment layers, wherein the firstand the second alignment layers comprise a reacted photopolymer, andwherein the liquid crystal molecules corresponding to a single pixel aredivided into four domains.
 2. The liquid crystal display of claim 1,wherein the first alignment layer comprises a first portion pre-tiltedin a first direction and a second portion pre-tilted in a seconddirection opposite the first direction, and wherein the second alignmentlayer comprises a third portion pre-tilted in a third direction crossingthe first direction and a fourth portion pre-tilted in a fourthdirection opposite the third direction.
 3. The liquid crystal display ofclaim 2, wherein the liquid crystal molecules are aligned with a slopeof a counterclockwise direction in the single pixel.
 4. The liquidcrystal display of claim 1, wherein the first alignment layer comprisesa first portion, a second portion, a third portion, and a fourth portionwith a first pre-tilt direction, a second pre-tilt direction, a thirdpre-tilt direction, and a fourth pre-tilt direction, respectively, andwherein the second alignment layer comprises a fifth portion, a sixthportion, a seventh portion, and an eighth portion with the firstpre-tilt direction, the second pre-tilt direction, the third pre-tiltdirection, and the fourth pre-tilt directions, respectively.
 5. Theliquid crystal display of claim 4, wherein the liquid crystal moleculesare aligned with a slope from four corners of the single pixel to acenter of the single pixel.
 6. The liquid crystal display of claim 1,further comprising a pixel electrode disposed between the first paneland the first alignment layer, wherein the pixel electrode does not havea cutout, a protrusion, or a slit.
 7. A method for manufacturing aliquid crystal display, comprising: providing a first panel comprising afirst alignment layer; providing a second panel comprising a secondalignment layer; providing a liquid crystal assembly comprising: thefirst panel, the second panel, and a liquid crystal layer comprising aliquid crystal material, a monomer, and a photo initiator disposedbetween the first panel and the second panel; and polymerizing themonomer by irradiating the liquid crystal assembly with ultravioletrays, thereby forming a polymer, wherein the liquid crystal materialcomprises liquid crystal molecules, wherein liquid crystal molecules arealigned with a pre-tilt angle of 88-89 degrees with respect to thesurface of the first panel and the second panel by the alignmentstructure of the first alignment layer and the second alignment layer,wherein the first and second alignment layers comprise a reactedphotopolymer, and wherein the liquid crystal molecules corresponding toa single pixel are divided into four domains.
 8. The method of claim 7,wherein the irradiating the first and the second alignment layers useslinearly polarized ultraviolet rays and a photo mask to selectively formvarious pre-tilt directions.
 9. The method of claim 8, wherein firstalignment layer comprises an alignment structure made by firstlyirradiating the first alignment layer with ultraviolet rays to form apre-tilt angle in a first direction and secondly irradiating the firstalignment layer with ultraviolet rays to form a pre-tilt angle in asecond direction opposite the first direction, and wherein the secondalignment layer comprises an alignment structure made by thirdlyirradiating the second alignment layer with ultraviolet rays to form apre-tilt angle in a third direction crossing the first direction andfourthly irradiating the second alignment layer with ultraviolet rays toform a pre-tilt angle in a fourth direction opposite the thirddirection.
 10. The method of claim 9, wherein the liquid crystalmaterial comprises liquid crystal molecules, and wherein the liquidcrystal molecules are aligned with a slope of a counterclockwisedirection in the single pixel.
 11. The liquid crystal display of claim8, wherein the first alignment layer comprises an alignment structuremade by repeatedly irradiating the first alignment layer withultraviolet rays to form a pre-tilt angle with a first direction, asecond direction, a third direction, and a fourth direction,respectively, and wherein the second alignment layer comprises analignment structure made by repeatedly irradiating the second alignmentlayer with ultraviolet rays to form a pre-tilt angle with the firstdirection, the second direction, the third direction, and the fourthdirection, respectively.
 12. The liquid crystal display of claim 11,wherein the liquid crystal material comprises liquid crystal molecules,and wherein the liquid crystal molecules are aligned with a slope fromfour corners of the single pixel to a center of the single pixel. 13.The method of claim 7, wherein the contents of the photo initiator arein a range from 0.01 to 0.1 wt % with respect to the contents of theliquid crystal material.
 14. The method of claim 13, wherein the photoinitiator comprises 2,2-dimethoxy-1,2-diphenyl ethanone.
 15. The methodof claim 7, wherein the contents of the monomer are in a range from 0.01to 10 wt % with respect to the contents of the liquid crystal material.16. The method of claim 15, wherein the monomer comprises an acrylatebased compound.
 17. The method of claim 7, wherein the intensity of theultraviolet rays is in a range from 2 to 20 J/cm² when the monomer ispolymerized.
 18. The method of claim 7, wherein a voltage of 2-20 V isapplied to the first panel and the second panel when polymerizing themonomer.